Function handle_output_tool 

pub fn handle_output_tool(
    args: &Value,
    spec: Option<&OutputSpec>,
    validators: Option<&OutputValidators>,
    stage: &str,
    now: i64,
    workdir: Option<&Path>,
    window: &mut ContextWindow,
) -> (String, Option<FinalOutput>)

Apply a submit_output call.

Returns the result text the model sees, and the recorded output when the submission was accepted. None means nothing was recorded and the model has been told why, so the caller must leave any previously submitted output in place: a rejected correction should not erase a good answer.

spec is the shape resolved for this stage (agent, stage, and caller combined). None means no level asked for a particular shape, which is not an error - the stage still wanted an answer, just not a specific form.